Eczema and dermatitis: Investigations

Investigations

Each pattern of eczema needs a different line of inquiry.

Exogenous eczema

Here the main decision is whether or not to under-take patch testing  to confirm allergic contact dermatitis and to identify the allergens responsible for it. In patch testing, standardized non-irritating con-centrations of common allergens are applied to the normal skin of the back. If the patient is allergic to the allergen, eczema will develop at the site of contact after 48–96 h. Patch testing with irritants is of no value in any type of eczema, but testing with suitably diluted allergens is essential in suspected allergic con-tact eczema. The technique is not easy. Its problems include separating irritant from allergic patch test reactions, and picking the right allergens to test. If legal issues depend on the results, testing should be carried out by a dermatologist who will have the stan-dard equipment and a suitable selection of properly standardized allergens (see Fig. 3.7). Patch testing can be used to confirm a suspected allergy or, by the use of a battery of common sensitizers, to discover unsus-pected allergies, which then have to be assessed in the light of the history and the clinical picture. A visit to the home or workplace may help with this.

Photopatch testing is more specialized and facilities are only available in a few centres. A chemical is applied to the skin for 24 h and then the site is irradiated with a suberythema dose of ultraviolet irradiation; the patches are inspected for an eczematous reaction 48 h later.

Other types of eczema

The only indication for patch testing here is when an added contact allergic element is suspected. This is most common in gravitational eczema; neomycin, framycetin, lanolin or preservative allergy can per-petuate the condition and even trigger dissemination. Ironically rubber gloves, so often used to protect eczematous hands, can themselves sensitize..

Patients with atopic dermatitis often have multiple type I reactions to foods, danders, pollens, dusts and moulds. Some find the measurement of serum total immunoglobulin E (IgE), and of IgE antibodies specific to certain antigens, not only useful in diagnosing the atopic state, but also helpful when advising on the role of dietary and environmental allergens in causing or perpetuating atopic dermatitis, particularly in chil-dren. Total and specific IgE antibodies are measured by a radioallergosorbent test (RAST). Prick and RAST testing give similar results but many now prefer the more expensive RAST test as it carries no risk of anaphyl-axis, is easier to perform and is less time consuming.

If the eczema is worsening despite treatment, or if there is much crusting, heavy bacterial colonization may be present. Opinions vary about the value of cultures for bacteria and candida, but antibiotic treatment may be helpful. Scrapings for microscopical examination  and culture for fungus will rule out tinea if there is clinical doubtaas in some cases of discoid eczema.

Finally, malabsorption should be considered in otherwise unexplained widespread pigmented atypical patterns of endogenous eczema.

Acute weeping eczema

This does best with rest and liquid applications. Non-steroidal preparations are helpful and the techniques used will vary with the facilities available and the site of the lesions. In general practice a simple and con-venient way of dealing with weeping eczema of the hands or feet is to use thrice daily 10-min soaks in a cool 0.65% aluminium acetate solution asaline or even tap water will do almost as wellaeach soaking being followed by a smear of a corticosteroid cream or lotion and the application of a non-stick dressing or cotton gloves. One reason for dropping the dilute potassium permanganate solution that was once so popular is because it stains the skin and nails brown.

Wider areas on the trunk respond well to cortico-steroid creams and lotions. However, traditional rem-edies such as exposure and frequent applications of calamine lotion, and the use of half-strength magenta paint for the flexures are also effective.

An experienced doctor or nurse can teach patients how to use wet dressings, and supervise this. The aluminium acetate solution, saline or water, can be applied on cotton gauze, under a polythene covering, and changed twice daily. Details of wet wrap tech-niques are given below. Rest at home will help too.

Wet wrap dressings

This is a labour-intensive, but highly effective tech-nique, of value in the treatment of troublesome atopic eczema in children. After a bath, a corticosteroid is applied to the skin and then covered with two layers of tubular dressingathe inner layer already soaked in warm water, the outer layer being applied dry. Cotton pyjamas or a T-shirt can be used to cover these, and the dressings can then be left in place for several hours. The corticosteroid may be one that is rapidly metabolized after systemic absorption such as a beclomethasone (beclometasone) diproprionate oint-ment diluted to 0.025% (available only in the UK). Alternatives include 1 or 2.5% hydrocortisone cream for children and 0.025 or 0.1 % triamcinolone cream for adults. The bandages can be washed and reused. The evaporation of fluid from the bandages cools the skin and provides rapid relief of itching. With improvement, the frequency of the dressings can be cut down and a moisturiser can be substituted for the corticosteroid. Parents can be taught the technique by a trained nurse, who must follow up treatment closely. Parents easily learn how to modify the tech-nique to suit the needs of their own child. Side-effects seem to be minimal.

Subacute eczema

Steroid lotions or creams are the mainstay of treat-ment; their strength is determined by the severity of the attack. Vioform, bacitracin, fusidic acid, mupirocin or neomycin can be incor-porated into the application if an infective element is present, but watch out for sensitization to neomycin, especially when treating gravitational eczema.

Chronic eczema

This responds best to steroids in an ointment base, but is also often helped by non-steroid applications such as ichthammol and zinc cream or paste.

The strength of the steroid is important (Fig. 7.6). Nothing stronger than 0.5 or 1% hydrocortisone ointment should be used on the face or in infancy. Even in adults one should be reluctant to prescribe more than 200 g/week of a mildly potent steroid, 50 g/week of a moderately potent or 30 g/week of a potent one for long periods. Very potent topical steroids should not be used long-term.

Bacterial superinfection may need systemic antibi-otics but can often be controlled by the incorporation of antibiotics, e.g. fusidic acid, mupirocin, neomycin or chlortetracycline, or antiseptics, e.g. Vioform, into the steroid formulation. Many proprietary mixtures of this type are available in the UK. Chronic localized hyperkeratotic eczema of the palms or soles can be helped by salicylic acid (1–6% in emulsifying oint-ment) or stabilized urea preparations.

Systemic treatment

Short courses of systemic steroids may occasionally be justified in extremely acute and severe eczema, par-ticularly when the cause is known and already elim-inated (e.g. allergic contact dermatitis from a plant such as poison ivy). However, prolonged systemic steroid treatment should be avoided in chronic cases, particularly in atopic eczema. Hydroxyzine, doxepin, trimeprazine and other antihistamines  may help at night. Systemic antibiotics may be needed in widespread bacterial superinfection. How-ever, Staphylococcus aureus routinely colonizes all weeping eczemas, and most dry ones as well. Simply isolating it does not automatically prompt a prescrip-tion for an antibiotic, although if the density of organ-isms is high, usually manifest as extensive crusting, then systemic antibiotics can help.